492 DR GEORGE WILSON ON THE ACTION OF THE DRY GASES 



in drying gases. But organic solids, such as litmus and colouring matter, though 

 probably more readily dried than gases, are certainly with difficulty rendered an- 

 hydrous. The difficulty is too familiar to every chemist who has made organic 

 analyses, to call for any illustration or proof Reference has akeady been made 

 to the desiccating power of ciu-rents of air, and to the likelihood of a solid being 

 more effectually dried by a gas than a gas by a solid. If, however, it is impos- 

 sible to supply a current of perfectly dry air, it may be doubted whether it is pos- 

 sible to render a solid anhydrous by passing air over it. It is difficult to imagine 

 that air, containing ex hypothesi some moisture, should make a solid absolutely 

 dry, drier than the air itself is ; yet it is not impossible that it should. The ten- 

 sion which heat gives to water- vapour ; its great dilatation when present in small 

 quantity ; and its diffusion through a large volume of gas, may more than balance 

 any power on the part of the solid to attract or condense it. There may be a limit 

 to condensation, as well as to vaporisation. 



Notwithstanding all that has been urged in this section, in reference to the 

 difficulty of rendering gases absolutely dry, it will not, I think, be questioned, that 

 in the experiments I have recorded, a close approximation to actual dryness was 

 attained in many of the trials. And, conceding that traces of moisture may have 

 been present, I may, nevertheless, with some justice, argue, that if the removal 

 of a certain amount of water from gases arrests for months their action on colours, 

 afortiari, the total abstraction of moisture would still more decisively negative 

 that action. 



VI. On the Action on D)y Organic Colouring Matters of the liquefied Anhydrou 

 Gases, and of Chlorine dissolved in liquids containing no Oonigen. 



The second series of experiments, as I have already mentioned, Avas made with 

 the view of ascertaining in what way water acts, when it accelerates the action 

 on colouring matter of the gases referred to, but particularly of chlorine. Accord- 

 ing to the prevailing theories of chemists, when water meets dry carbonic and 

 sulphurous acid, or dry ammonia, it does not merely dissolve them, but allows 

 its elements to be appropriated by each of these gases, which become, in conse- 

 quence, compounds possessed of new relations to bases, acids, colouring matters, 

 and the like. I shall therefore set these gases aside, as not admitting of direct 

 comparison with chlorine, which chiefly concerns us. There is no reason, on the 

 other hand, for supposing tliat water does more than merely dissolve oxygen, 

 sulphuretted hydrogen, and hydrochloric acid, so that that liquid may be sup- 

 posed to change their relation to colours in the same way as it does that of 

 chlorine. 



The older chemists held by the axiom, " Corpora non agunt nisi soluta,' and 

 by means of it could fully have accounted for the difference in action on colours 



